The present invention relates to a method for controlling an injector via which a specified quantity of fuel is injected into the cylinder of an internal combustion engine.
Methods of fuel injection into an internal combustion engine, in particular in direct injection, are already known. For example, in a unit injector system (UIS), a control valve is controlled by a magnetically operated actuator in step with a trigger signal for injecting, under high pressure, a specified quantity of fuel into the combustion chamber of the engine. This creates the problem of also being able to inject the smallest possible controllable quantities of fuel. These small quantities are on the order of magnitude of up to 2 mm3 for all operating conditions. In the case of the known magnetically controlled actuators, these small quantities cannot be achieved, especially when the engine runs at high rotational speeds, since the control valve is only adjustable to a limited extent in intermediary positions between the open and closed states. Piezoelectric actuators, on the other hand, control the injected quantity only via a constant opening cross-section, formed between the control valve and its seat in the intake channel.
The method according to the present invention for controlling an injector has the advantage over the related art that, for controlling the fuel quantity, the trigger signal for the actuator is adjustable in amplitude as well as in duration. This has the advantage that it is possible to inject a small, precisely-metered fuel quantity not only at low RPMs and low load. It is also possiblexe2x80x94in particular when using a piezoelectric actuatorxe2x80x94to inject the quantity of fuel to be injected in a targeted manner and, as a function of engine load and rotational speed, in a defined manner, via the amplitude of the trigger voltage as well as the duration of the applied control signal. It is particularly advantageous that it is possible to also consider parameters containing engine-related, emission-relevant, and drive-specific components.
It is considered especially favorable that the trigger signal is initially selected in such a way that the control valve is in ballistic mode and therefore clears the opening cross-section of the intake channel. If the injection quantity is to be increased, the amplitude of the trigger signal is simply increased as well, with initially the same delivery duration, so that the opening cross-section of the inlet channel narrows. During this phase, the duration of the trigger signal remains constant.
To further increase the injection quantity, the control valve is advantageously switched to nonballistic mode. This makes is possible to achieve further increases in the quantity of fuel to be injected, even after the switchover to nonballistic mode.
It is also considered advantageous to increase the duration of the delivery until the quantity of fuel to be injected is larger than that which can be achieved with a closed control valve and short trigger signal. In this case, in order to achieve a favorable engine behavior, it is possible to provide at least one jump in the delivery duration and amplitude of the control signal in order to achieve a change in the determination of the quantity.
This makes it possible to select the maximum amplitude of the control signal with only one jump. Further increase in the injection quantity is then achieved by extending the duration of the delivery.
In an alternative embodiment, several jumps may be used, increasing the trigger voltage incrementally and adapting the delivery duration to the specified injection quantity with each jump.
It is also possible to advantageously increase the trigger signal up to its maximum value, with the control valve resting on the valve seat and sealing off the opening cross-section. In this case, further increase in the trigger signal does not result in an additional increase in the delivery quantity. Rather, the latter is achieved by extending the duration of the delivery.
An advantageous application of the method uses a piezoelectric actuator, which is used in particular in a direct-injection system.